The invention relates to a four-stroke internal combustion engine with compression ignition and internal exhaust gas recirculation, and to a method for the open-chain and closed-loop control of the engine process of a four-stroke internal combustion engine with compression ignition and internal exhaust gas recirculation.
A four-stroke internal combustion engine with compression ignition is known from the publication xe2x80x9cThe Knocking Syndromexe2x80x94Its Cure and Its Potentialxe2x80x9d by J. Willand, SAE Paper 982483. In a homogeneous combustion process described there for the internal combustion engine, parallel energy release by means of compression is achieved by decentralized activation of a charge located in a combustion space, in contrast to previously usual processes in which serial combustion of the charge with a gradually spreading flame front takes place due to central activation by means of an ignition source (spark-ignition process) or by means of injection (diesel process). The decentralized activation provides each charge element with sufficient activation energy to achieve the energy release level.
Particular advantages in the case of homogeneous combustion by means of decentralized activation of the charge follow from the possibility of being essentially able to burn extremely weak mixtures completely, so that the fuel consumption decreases. On the other hand, the combustion of such extremely weak mixtures is associated with low combustion temperatures, which are usually below the limiting temperature for the formation of oxides of nitrogen (NOx), so that the emissions of oxides of nitrogen of such an internal combustion engine are low, at least in the case of low load.
The self-ignition of the charge during the combustion process does, however, demand a certain charge energy and charge temperature level. As described in the publication cited for a four-stroke internal combustion engine, a certain quantity of hot exhaust gas from the previous cycle is retained in the combustion space for mixing with the fresh charge of the current cycle in order to bring the temperature in the combustion space to the necessary activation level. This takes place by appropriate control of the inlet and exhaust valves; in contrast to the usual valve timing, it is proposed that the exhaust valve should be closed earlier and that the inlet valve should be opened later. By this means, a certain quantity of residual exhaust gas can be retained in the combustion space for mixing with the fresh charge and for use in the next cycle. Because the reused residual exhaust gas proportion does not leave the combustion space or the inlet and exhaust ducts, a so-called xe2x80x9cexhaust gas retentionxe2x80x9d is realized in this way.
The type of exhaust gas retention described has the disadvantage that heat transfer takes place between the hot exhaust gas retained in the combustion space and the cylinder wall, which is cold relative to the exhaust gas, and the temperature of the exhaust gas therefore decreases. The desired increase in the temperature of the charge in the combustion space is then insufficient.
In addition, exhaust gas recirculation systems are known in which exhaust gas is returned from the combustion space into an intake duct by means of large valve overlaps, for example by early opening of the inlet valve, and this exhaust gas is sucked back from the intake duct into the combustion space. Because the intake duct is cold relative to the exhaust gas, however, undesirable cooling of the exhaust gas likewise occurs during the insertion and extraction into and from the intake duct. In addition, the suction system is heated by the hot exhaust gas and losses in volumetric efficiency therefore occur.
In contrast, the present invention is based on the object for the creating a four-stroke internal combustion engine with compression ignition and creating a method for the open-chain and closed-loop control of such an internal combustion engine, in which heat losses from the exhaust gas are substantially avoided during the exhaust gas recirculation.
The four-stroke internal combustion engine with compression ignition and the method for the open-chain and closed-loop control of such a four-stroke internal combustion engine have the advantage that because the exhaust gas is pushed from the combustion space through the open exhaust valve into the exhaust duct, in which the wall temperatures are higher than those of the cylinder wall, the exhaust gas cannot cool so much there and approximately retains its high temperature for the desired increase in the energy level of the charge.
If the charge-exchange top dead center position is defined by a crank angle of 360 degrees, a particularly preferable development of the invention provides for the inlet and exhaust valves to have the following timing: opening of the exhaust valve within a crank angle range between 90 degrees and 180 degrees, preferably at 150 degrees; closing of the exhaust valve and essentially simultaneous opening of the inlet valve within a crank angle range between 450 degrees and 540 degrees, preferably at 470 degrees; and closing of the inlet valve within a crank angle range between 540 and 630 degrees, preferably at 560 degrees.
Preferably, the inlet and exhaust valves are electromagnetic valves which can be actuated by an open-chain and closed loop control device in such a way that, as a function of the parameters of beginning and duration or the center point of the combustion/conversion of the charge during a cycle, which parameters form the control parameters, as setting parameters a certain quantity of exhaust gas can be recirculated into the combustion space and a certain temperature of the recirculated exhaust gas can be achieved in order to determine beginning and duration of the combustion/conversion of the charge for the respectively next cycle. Because of the importance of the quantity and temperature of the exhaust gas recirculated into the combustion space to the beginning and duration of the combustion/conversion of the charge, as part of the combustion process, it is then possible to adjust to particularly low consumption and low-exhaust gas combustion conditions. The variable timing of the inlet and exhaust valves is within the quoted, preferred crank angle ranges. In accordance with a particular embodiment of the invention, it is also possible to configure the inlet and exhaust valves so that they can be actuated electrohydraulically.
Embodiment examples of the invention are represented in the drawings and are explained in more detail in the following description.